Polyimides have been widespread use in the electronics industry, such as flexible printed circuit boards, tape automated bonding (TAB) and thin film package, due to the properties of high heat resistances and low dielectric constant. However, polyimides possess the disadvantage of lower adhesion to copper. An additional adhesive should be applied between copper foil and polyimides film to improve the bonding strength. Since the heat resistance of the adhesive used was weaker than that of polyimides substrate, the resulted flexible printed circuit board and tape automated bonding (TAB) will exhibit poor quality. To develop a construction with non-adhesive will greatly improve the overall performance.
The use of a modified polyimide to enhance the bonding strength between polyimide substrate and copper foil has been disclosed by prior art, such as Japanese Kokai Tokkyo Koho JP 62-278687 and SAMPE Journal July/August 1988. These known references described that the adhesion of polyimide substrate was improved by the incorporation of siloxane segments into a polyimide backbone polymer. However, siloxane incorporation will greatly reduce glass-transition temperature of polyimide and cause phase-separation phenomenon. Therefore, an homogeneous polyimide film cannot be produced.
Japanese Kokai Tokkyo Koho JP 61-48318 and 62-141077 disclosed incorporating bismaleimides into polyimides material for improving thermal resistance of the final product. However, these prior Patents did not effectively enhance the adhesion between copper foil and polyimide substrate.